When plants are in hot environments they'll close stomata to prevent water loss. This closing of stomata leads to low levels of CO2 which leads to photorespiration. But where is the oxygen coming from for photorespiration? In my textbook it says that it is coming from photolysis during the light-dependent stage of photosynthesis. However, surely if the stomata are closed, transpiration stops and so the level of water in the plant decreases????

JackBean wrote:Second, water is mainly transported from roots and evaporated through stomata. Thus closing stomata does not reduce intake of water.

Pedantry: I thought the evaporation of water through the stomata creates suction which is one of the several mechanisms that draw water upwards into the leaves (the other mechanisms being capillary action and osmotic pressure). So closing the stomata DOES reduce the intake of water.